Do not trust what you see on the outside
Remove the caps to see what’s inside (you can slide them back on again). Minor differences on the outside can mean major differences on the inside (even if the outsides appear identical). The antenna size can be different but even the type of antenna can be completely different (I know because I have opened most of my antenna’s).
(To remove the cap: bend the plastic ‘up and down’ to the sides while pulling it off. Some caps come off very easily while others require more strength to remove).
Note: Removing the caps of the foldable antenna types will require more craftsmanship and subtle finicking (at least if you want to be able to put it back on) and will require more force.
Many of these ‘Chinese antenna’s’ may not be specifically for 868MHz at all, some are used for GSM 900/1800 MHz, and the antennas that are inside can be very different between one make and another.